<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div id="app">
        <!-- <h3>
            {{ val + "!!!!" }}
        </h3>
        <h3>
            {{ val + "!!!!" }}
        </h3>
        <h3>
            {{ val + "!!!!" }}
        </h3> -->

        <!-- <h3>
            {{ changeVal() }}
        </h3>
        <h3>
            {{ changeVal() }}
        </h3>
        <h3>
            {{ changeVal() }}
        </h3> -->

        <input v-model="val" type="text">

        <h3>
            {{ newVal }}
        </h3>

        <h3>
            {{ newVal }}
        </h3>

        <h3>
            {{ newVal }}
        </h3>

        <button @click="fn">按钮</button>
    </div>

    <script src="./vue.js"></script>

    <script>
        new Vue ({
            el : "#app" ,
            data : {
                val : "我是初始数据"
            },
            methods : {
                changeVal (){
                    console.log( 1 );
                    return this.val + "!!!!"
                },
                fn (){
                    console.log( this );
                }
            },
            // 计算属性 --- ( 添加到this)
            // 必须要return

            // 1. 缓存
            // 2. 当依赖项不发生改变是不会重新进行计算
            computed : {
                newVal (){
                    console.log( 1 );
                    return this.val + "!!!!"
                }
            }
        })
    </script>
</body>
</html>